Synthesis Of Carbon Nanotubes And Carbon Encapsulated Metal Nanoparticles By Laser Irradiation

Carbon nanotubes and carbon encapsulated metal nanoparticles are popular carbon materials; they show potential applications in many fields such as biomedical engineering, catalysis and new energy, etc.In this thesis, we synthesized multi-walled carbon nanotubes by millisecond pulsed laser ablation in ethanol under ambient temperature and pressure and the formation mechanism of carbon nanotubes was studied. The capabilities of providing carbon atoms are different for carbon black and graphite. As laser ablates on carbon black/nickel target, a huge vapor plume was formed over the target which results in a heat affected zone around the plume and provides carbon atoms, carbon nanotubes can grow in the heat affected zone where the nickel nanopartilces were stable and can serve as catalysts. While the vapor plume produced from graphite/nickel target was too small and far away from the heat affected zone where the catalyst nanoparticles can stably exists, carbon nanotubes cannot form under such a condition. In addition, carbon nanotubes produced from carbon black were flexible and with many dangling carbon atoms on the tube suface, which is beneficial for combination as the carbon nanotubes form composites with matrix and improve the mechanical properties.Carbon encapsulated nickel nanoparticles (CENPs) with high purity were fabricated by microsecond pulsed laser ablation of nickel target in ethanol. The size of CENPs varies from tens to hundreds nanometers, and the CENPs show two kinds of typical morphology, i.e., single carbon shell and double carbon shell. Based on the TEM observation, a mechanism of CENPs formation was proposed, that is, laser irradiation induced the decomposition of ethanol and evaporation of the nickel target, the generated carbon atoms mixed with nickel vapor at high temperature, and then Ni/C liquid particles appeared during the cooling period, finally, the carbon shells formed by precipitation of carbon atoms on the surface of nickel cores, which leads to the formation of CENPs. This method can also be used for the synthesis of other core/shell nanostructures.